he Earth Observing System (EOS) is a series of polar-orbiting and low-inclination satellites for long-term global observations of the land surface, biosphere, solid Earth, atmosphere, and oceans, and is the centerpiece of Mission to Planet Earth (MTPE). In tandem with EOS, platforms from Europe, Japan, and US will establish an international Earth-observing capability that will operate for at least 15 years and allow scientists to obtain information covering all major Earth system processes.
SOLSTICE II is one of 20 instruments selected for flight and will be designed, built, and operated at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado, Boulder.
EOS SOLSTICE Project Overview
OS SOLSTICE or SOLSTICE II will provide precise daily measurements of the full-disk solar ultraviolet (UV) irradiance between 5 and 440 nm. The sun's UV radiation is the dominant energy source to the Earth's atmosphere, where small changes in the radiation field have an important effect on atmospheric temperature, chemistry, structure, and dynamics. Moreover, even small alterations in the atmosphere (e.g., small changes in total ozone) can produce dramatic differences in the solar radiation reaching the Earth's surface. Measuring small changes in solar UV irradiance will improve understanding of corresponding changes in the photochemistry, dynamics, and energy balance of the middle atmosphere. Changes resulting from the 27-day solar rotation and the 11-year solar cycle will receive emphasis, as will those arising from solar flare incidents. SOLSTICE II will continue the UV observations initiated by its predecessor aboard the Upper Atmosphere Research Satellite (UARS).
The SOLSTICE II instrument consists of a five channel spectrometer together with the required gimbal system to point the instrument at the sun and selected stars. The stellar targets, observed with the same optics and detectors as those directed at the sun, are essential for they determine the long-term drift correction to the SOLSTICE II calibration. The ensemble average flux from these 30 or so bright early-type stars should remain absolutely constant over arbitrarily long time periods. This unique method thereby establishes the instrument response as a function of time throughout the EOS mission and yields time series of solar variability that are completely corrected for instrumental drift.
The investigation will also model the penetration of solar radiation down into the Earth's atmosphere and establish the radiation field at all locations and altitudes, including the Earth's surface. In certain wavelength intervals, the depth of penetration varies dramatically due to details in the atmospheric absorption, and calculations require solar data with very high spectral resolution. To accommodate these measurements, a separate, high-resolution spectrometer channel is included. The standard SOLSTICE II data product will be a daily average of the solar UV irradiance from 5 to 440 nm. More specifically, data products will consist of solar UV irradiance from 30 to 440 nm, the solar UV irradiance from 115 to 320 nm at much higher resolution, and extreme UV irradiance between 5 and 20 nm.